Refrigerated display merchandisers, also commonly referred to as display cases, having open display regions are commonly used in supermarkets, mini-marts, convenience stores and other commercial establishments for displaying and merchandising refrigerated or frozen products for sale. The open nature of such display cases permits the consumer to simply reach into the product display region to select and remove a product for purchase without the inconvenience of needing to open a door to access the product. Customarily, in open front display cases, at least a single curtain of cold refrigerated air is passed downwardly at a relatively high velocity across the open front of the display case to form an invisible barrier between the product display region and the region of the store in front of the display case. This air curtain not only helps retain cool refrigerated air within the product display region of the display case, thereby cooling the display product on the shelves of the display case, but also functions to isolate, to a certain extent, the product display region from the ambient air within the store. Ambient air that does enter into open product display region undesirably causes increased energy consumption by increasing the cooling demand on the refrigeration system associated with the display case. Further, such ambient air may also cause a local temperature rise within the product display region sufficient to result in an undesirable rise in product temperature that could adversely impact upon product quality.
A problem encountered with when passing a curtain of refrigerated air downwardly across the open front of the product display region of the display case lies in the entrainment of ambient air into the stream of refrigerated air forming the air curtain. Turbulence exists at the boundary between the relatively high velocity curtain air and the generally quiescent ambient air lying in front of the display case. As a result of such turbulence, some ambient air is undesirably entrained into the air curtain.
Multiple air curtain display cases have been developed in the prior art to address this entrainment problem. For example, display cases having two adjacent, parallel, but independently generated, air curtains of refrigerated air are common in the art. Typically, such as disclosed by Maehara in U.S. Pat. No. 4,633,677, the outermost air curtain has a slightly higher temperature than the innermost air curtain, so as to protect the colder innermost air curtain from the impact of ambient air entrainment.
Also, it is well known in the art to establish a third air curtain of relatively high temperature ambient air outwardly of one or two refrigerated air curtains as a means of reducing entrainment of ambient air from the store into the refrigerated air curtains. Abraham, in U.S. Pat. No. 4,267,706, Brown in U.S. Pat. No. 3,812,684, and MacMaster et al in U.S. Pat. No. 3,517,526, each disclose establishing an ambient air curtain outwardly of an innermost refrigerated air curtain, with the outer ambient air curtain being directed downwardly parallel to and adjacent to the inner refrigerated air curtain. Beckwith et al, in U.S. Pat. Nos. 3,648,482; 3,850,003 and 3,937,033; MacMaster et al, in U.S. Pat. No. 3,827,254 and Roberts, in U.S. Pat. Nos. 5,345,778 and 5,357,767, each disclose establishing an ambient air curtain outwardly of a pair of refrigerated air curtains. The curtain closest the product display region of the display case is coolest, while the center curtain is at a temperature slightly warmer than the innermost curtain, but substantially cooler than the outermost ambient air curtain. The center curtain of warmer refrigerated air serves to buffer the innermost colder refrigerated air curtain from warm air intrusion from the outermost ambient air curtain. The outermost curtain of ambient air is directed substantially vertically downwardly, either parallel to and adjacent the center air curtain or slightly inwardly toward the center air curtain, so as to preclude refrigerated air from the center and innermost refrigerated air curtains from spilling out of the product display region of the display case. The outermost ambient air curtain itself ideally spills into the store near the base of the display case so as to not be drawn into the air return inlets through which the refrigerated air curtains return to the evaporator compartment.
In conventional practice, the ambient air curtain is established by drawing ambient air by means of one or more fans from the store environment into a plenum located in the forward portion of the top wall of the display cabinet of the merchandiser. Then ambient air discharges from the plenum through a grid to form the air curtain. The grid serves to direct the ambient air curtain along a desired path to the outside of one or more inner curtain of cooler refrigerated air. Conventionally, the inlet duct to the plenum through which the ambient air is drawn forms a relatively short and relatively direct path through the top wall of the display cabinet. A shortcoming of an admission assembly of this type lies in the tendency of the air flow discharging through the grid to be non-uniform along the length of the display case. The resultant non-uniformity in the air curtain degrades the overall effectiveness and performance of the air curtain. Thus, although generally effective to substantially reduce the amount of entrainment of ambient air into the recycled refrigerated air as compared to a single air curtain design, significant improvement in overall air curtain effectiveness can be achieved by providing an improved ambient air admission assembly that ensures a generally uniform flow distribution in the resultant air curtain along the length of the display case.